1. Field of the Invention
This invention relate to surgical needles, and more particularly to needles used in phaco-emulsification procedures during eye surgery.
2. Description of Related Art
In a number of surgical procedures, the tip of a small needle is inserted into body tissue or a cavity and used to remove unwanted material, often with the assistance of ultrasonic mechanical vibration. One prominent example of this type of application is the phaco-emulsification procedure, adopted several decades ago, for the removal of cataracts and other material from the capsular bag of the eye, particularly to facilitate an artificial lens implant. In the earliest examples of this procedure, a straight needle was inserted through a small incision into the capsular bag, and ultrasonic oscillation of the needle tip caused the tip to contact and mechanically emulsify the material. In addition, the ultrasonic oscillation of the needle tip in the liquid of the capsular bag caused a small amount of cavitational emulsification of the material.
An aspiration bore in the center of the needle drew out the material as it was emulsified. The suction effect of the aspiration flow in the aspiration bore created a pressure differential between the inside and outside of the needle and caused material to occlude at, and adhere to, the needle tip, an effect that was generally beneficial because the adhesion helped the tip contact and mechanically emulsify the adhering material. In addition, the peristaltic pump that generated the aspiration flow would increase the suction upon detection of an occlusion, thereby facilitating removal of the occlusion. The aspiration of emulsified material concurrent with the emulsification process enabled the complete procedure to be effected within a relatively short interval. Due to the small incisions and limited invasiveness, there were minimal side effects and very short recovery time under ideal conditions.
Ideal conditions, however, were rarely available, and as many thousands of these operations were completed, it was found desirable to use one or more of a number of variations for different purposes, not all of which are compatible. For example, the interior volume of the capsular bag is of maximum depth in the mid-region, into which a straight needle can conveniently be inserted. Alongside the incision in the anterior capsular bag wall and in the corners of the capsular bag, however, access can better be obtained by a curved or bent needle. Accordingly, a number of different variants on the curved needle were introduced, as evidenced in part by U.S. Pat. Nos. 4,750,488; 4,301,802; 4,136,700; 5,154,694 and 5,417,654, in which different variations were used for different purposes and advantages. In addition, it was found that curved or bent needles could improve cavitational emulsification, because cavitation increases when the larger surface area presented by the side of the curved or bent needle moves in opposition to the material. Some of the curvatures were also intended to reduce the danger that the cutting edge of the tip would encounter and damage the rear wall of the capsular bag as the needle was manipulated within the capsular bag.
Such changes, however, introduce other problems and limitations in practical situations. Conventional needles have a sloping face terminating in a sharp point to aid in puncturing tissue. Simply bending such a needle to a desired angle may result in the sharp point facing the capsular bag wall in certain needle orientations, thereby increasing the chance of damage to the capsular bag wall.
A curved or bent needle also decreases the surgeon's visibility of the needle tip. Typically, a surgeon operates from above the eye, pointing the needle downward into the eye with the bend in the needle pointing downward. When viewed from above, the tip of a needle with a severe bend tends to disappear underneath the body of the needle, decreasing its visibility and increasing the danger of positioning error by the surgeon.
In addition, the aspiration bore of bent or curved needles often faces away from the direction of reciprocation, and thus does not present a large opening in the direction of reciprocation upon which the material may be occluded. Furthermore, the sharp point created by the sloping face of bent conventional needles may not allow the aspiration bore to be placed in close proximity to material in certain orientations, thereby decreasing occlusion of material at the aspiration bore. The bend of the needle also increases frictional contact of the aspiration flow with the interior walls of the needle, which increases flow resistance, decreases the aspiration rate, and reduces the occlusion of material at the aspiration bore. The reduced occlusion and adhesion of material to the needle tip resulting from bent or curved needles ultimately decreases the efficiency of emulsification, increases the required operating time, and increases the possibility of heat damage or other damage to the eye. To offset the reduced occlusion of bent needles, aspiration pressure may be increased. However, increased aspiration pressure makes the phaco-emulsification procedure less controllable and increases the danger of collapsing the capsular bag.
The effect of curved or bent needles on capsular bag access, cavitational emulsification, puncture avoidance, tip visibility, aspiration rate, occlusion, and mechanical emulsification therefore varies as the curvature or bend in the needle increases. As the curvature or bend increases, capsular bag access and cavitational emulsification increase, while tip visibility, aspiration rate, occlusion, and mechanical emulsification generally decrease. Consequently, there is a need for a needle offering the advantages of better cavitational emulsification, easier manipulation and access within the capsular bag, and lessened chance of unintended puncturing of the back wall of the capsular bag, while at the same time providing an aspiration bore orientation and flow rate that facilitates occlusions at the needle tip and enhanced mechanical emulsification.